Plasma display panels (hereinafter referred to as “PDPs”) allow definition and screen size to be increased, so that 65-inch class televisions (TVs) have been commercialized.
A PDP is basically formed of a front plate and a back plate. The front plate has the following elements:                a glass substrate made of sodium borosilicate glass using a float method;        a display electrode that is formed on a main face of the glass substrate and includes a stripe-like transparent electrode and a bus electrode;        a dielectric layer that covers the display electrode and serves as a capacitor; and        a protective layer that is formed on the dielectric layer and is made of magnesium oxide (MgO).While, the back plate has the following elements:        a glass substrate;        a stripe-like address electrode formed on a main face of the glass substrate;        a base dielectric layer for covering the address electrode;        barrier ribs formed on the base dielectric layer; and        phosphor layers that are formed between the barrier ribs and emit red light, green light, and blue light, respectively.        
The front plate and back plate are stuck to each other while the sides having an electrode are faced to each other, and the periphery of them is air-tightly sealed with a sealing material. Discharge space partitioned by the barrier ribs is filled with discharge gas of Ne—Xe at a pressure of 400 to 600 Torr. In the PDP, a video signal voltage is selectively applied to the display electrode to cause discharge, ultraviolet rays that are generated by the discharge excite respective phosphor layers to emit red light, green light, and blue light, and thus a color image is displayed.
As the dielectric layers, low-melting glass mainly made of lead oxide is used. As the sealing material, also, low-melting glass mainly made of lead oxide is used. In consideration of recent environmental issues, examples of dielectric layers containing no lead component are disclosed in Japanese Patent Unexamined Publication No. 2003-128430, Japanese Patent Unexamined Publication No. 2002-053342, Japanese Patent Unexamined Publication 2001-045877, and Japanese Patent Unexamined Publication No. H9-050769.
An example of phosphoric-acid-based sealing material containing no lead component and an example of bismuth-oxide-based sealing material are disclosed in Japanese Patent Unexamined Publication No. 2004-182584 and Japanese Patent Unexamined Publication No. 2003-095697.
Recently, PDPs have been increasingly applied to high definition TVs where the number of scanning lines is two or more times that in a conventional National Television Standards Committee (NTSC) method, and PDPs containing no lead component have been demanded in consideration of recent environmental issues.
Sealing material mainly made of phosphoric-acid/tin-oxide based low-melting glass that contains no lead component has a water resistance lower than that of lead-oxide-based sealing material, so that the air-tightness of the PDPs cannot be kept sufficiently, disadvantageously.
When the conventional sealing material made of bismuth-oxide-based glass is used, bismuth oxide reacts with silver materials in the display electrode on the front plate and the address electrode on the back plate to generate many air bubbles, and hence the air-tightness of the PDPs cannot be kept sufficiently, disadvantageously. Especially, in high-definition PDPs of the high-definition TVs or the like where the number of scanning lines is two or more times that in the conventional art, the number of electrodes is increased and hence the disadvantage becomes remarkable.